Optical device for image display



Julyllf 1951 J. A. @ma @Mff- OPTICAL DEVICE FOR IMAGE DISPLAY Fileduly 25, 1957 5 sneeis-sheet 2 )IHwillllllllllmlllmlllmllllllmlllllllllllllllll 1| INVENTOR.

JAMES A. OGLE JUlYl-l', 1961 l J. A. @SLE y OPTICAL DEVICE F'OR IMAGE DISPLAY Fneduuly 25, 1957 5 sheets-sheet s 6 RM E wd A m m WN. E A M www@ July 4'11, 1961 .5. A. @Gm

OPTICAL DEVICE FOR IMAGE DISPLAY 5 Sheets-Sheet 4 Filed July 25, 195'? mvENToR. JAME A. OGLE ATTORNEY July l1, 1961 Y J. A. @Gm

1 OPTICAL DEVICE FOR XMAGE DSPLAY Filedduly 25, 19:57

5 Sheets-Sheet 5 lkw/EMDR.

JAMES A OGLE @www l 2,991,743 yOPTICAL DEVICE FOR GE DISPLAY lames A. Ogle, Paoli,l'a'., asslr to Bughs iCor poration, Detroit, Mich., n corporation ol Michigan yFiled July 25, 1957, Sei-.No 674,228 14 .i :no: (Cl. llt-43.5)

This invention relates to an optical display system-andmore particularly to an optical glide path indicator for visually indicating to a pilot the proper vglide angle for the safe landing of an aircraft on an area of restricted size. y v

. Present day high speed aircraft have closing speeds at landing of the order of 100 knots. Normally the length of airport runways is about 6,000 feet and the pilot has ample time to make the necessary adjustments in his angle of descent toelect a safe landing. However, on landing areas of limited size such as the light desirs of modern aircraft carriers which vary from about 58@ ieetto about 900;A lt'eet in length, the'v problem of landing safely'becomes'severe. Y

An older method of assisting the pilot in landing his aircraft, and one which is still used extensively, utilises the services of a landing signall otiicer who stands toward the stern of the ship on the port side facing the oncoming aircraft and signals landing instructions to the pilot by means' of small Apaddles held in eachh. 1 These 'landing instructions become recognizable to .the pilot at a distance ofabout 500 feet from the ship. Obvious ly from what has been said regarding the kclosing speed of the aircraft and the length of the landing area, neither the Landing Signal Omcer northe pilot are able to perceive or correct small but significant errors in the aircrafts glide angle. 'y l A more precise method of aiding a pilot to dy his aircraft along a derined descent path is described by H. C. N. art in his U.S. Patent No. 2,784,925. This method comprises a mirror adapted to be positioned in-a elinably at the landing area to show to the pilotth'e image of a first iined marker arranged some distance in front of the mirror in suchl position that it is reilected by the mirror'. The pilots line of sight to the image of the rst fixed marker is arranged to coincide withfhis line ci sight to a directly y'visible second fined marker at'the land ing farea so as to, define the angley of the desired path `in elevation from the mirror.

The optical landing system of the instant invention consists of an assembly lhaving a viewing window oriented toward voncoming aircraft. The assembly consists of a plurality of cells; each of which comprise 'reference lights l and lenses so disposed with respect to one another that a virtual' image of the reference lights is produced. The

ted

lill

. Consequently an elevator is not required and. m'nce 2 lamps are reflected in the mirror. The instant invention utilizes internal reference lights and lenses thereby eliminating the external marker lampsand eeoting a savm ing in space, electrical lwiring and power.

'l'he characteristics of aircraft diiier appreciably with regard to the distance between the pilotsline of sight. and the hook on the underside of the aircraft adapted to engage one of` a plurality of arresting wires stretched about eight inches above the flight deck. In order .compensate for diierent hook-to-eye distances provide a safe touch-down point, the fmirror assembly mounted on an elevator which adjusts lfor vertical disc tances withrespect to the landing area while maintaining the same glide angle. The combined weight of mirrorv assembly and the elevator platform applied at deels height and offset from the center line 'of the ship is sdered highly undesirable from the standpoint of eta lf ity. The necessary hook-to-eye distances can be est lished conveniently through the use of the pres nt; vention' -byhorizontally spacing several of the indient along the edge of the landing area and actuating one the forward indicators for larger aircraft while smaller aircraft use indicators further aft on the landing area.

lens assembly weighs considerably less than a mir assembly, stability problems are minimized. Obvio too, a plurality of mirror assemblies cannot be horizon ly spaced along the landing area in an arrangemet similar to that previously described since the externa marker lights would be redected by allot the mirrors and there appears to be no convenient way of selectively actuating one of the indicators.

Another problem associated with the use oi visum landn ing aids is solar reection from the face of the indicator. lnthe case of the mirror, a very large percentage oi the light incident on the face of the mirror is reected tornano the oncoming aircraft. Any attempt to` eliminate the horizon results in a deviation fromthe speciiied path. 4In one embodiment of the present invention face of the indicator is made up of a plurality of cylin drically ribbed lenticulars whose primary function is horizontal spreading of the rays emerging trom the irnaigq ing lens. lnv addition these lenticular-s provide a random distribution of angles of reflection for the sun's rays which-fall upon the lens assembly with equal angles incidence. The resulting scatter of the reilected light reduces the apparent intensity of the redection to tolerable level. if it is desired to eliminate the -retleo tions completely, either of the following will be effective:

` inclining the lenticular spreaders with respect to the lens plurality of virtual imagesproduced by the cells are made to coincide and thepilot sees a single virtual image through the viewing window. The image of the lights as seen by the pilot is a horizontal bar of light which appears to move up `or down depending upon the aircrafts angle of approach. Associated with the assembly but external thereto are fixed rows of lights which establish a datum line.y The correct glide angle is indicated by the visual alignment of the bar of light with the datum line' Having made the necessary adjustments in his angle of dcent, the pilot is required only to maintain a steady course to achieve the proper touch-down point for a safe landing. l

The instantinvention possesses va number oi cant advantages over the prior art vmethods which' will be1 come apparent as the system is hereinafter described. The aforementioned mirror landing system utilizes a horizontal row of lamps spaced approximately l5@ to feet the mirror trained thereon so that assembly or inclining :the lens assembly with respect to its horizontal reference and then moving the internal reference lamps which causes the glide path to be raised or lowered relative to the lens assembly. This latter feature of optically reorienting the landing system be changing the relative position of the reference ln withrespect to the imaging lens is useful for pitch rection. Instead of controlling the movement of entire lens assembly, the stabilization means coupled directly to the lamp mounting'braclcet whi assembly remains in a fixed position on the landing The use of the instant invention is not restricted shipboard landings but rather its light weight, mor size, comparatively low power requirement which rr battery furnished, and its ease of operation mais@ it especially suitalble for use on land bases of restricted particularly for emergency landings.

Accordingly, it is a prime object oi the instant inve e tion to provide optical indicating means whereby speed aircraft can land safely on of restricted `proxixnately three or four degrees.

; an angle within whichI an observer stationed at the right ot thelens would be able to view the `virtual image. lf light source 40 is moved downward to the position 'designated 40a the image of the ilament now appears at '75a and the .light rays 76a, 77a and 78a define a vertical viewing angle which is displaced upward from that produced by light source 40 in its original position. ln eifect moving the light source downward with respect to the lens moves the virtual image of the source downward thereby requiring the observer to move upward with .respect to his original position if he is to keep the image inethod ot establishing the proper glide angle the maior axis oi the lens assembly may be fixed in a vertical plane while the light source is moved with repect to its associated. Fresnel lens. i

Each group of fou-r lamp filaments in a particular cell is imaged by its Fresnel lens at a distance of approximatelyv u feet behind the lens. The image of the lilarnents is thus a virtual image visible only through the pupil which is the periphery of the Fresnel lens associated with that group ot' four lamps. Assuming that a single lens was used, the observer would be able to view the image of the filaments through a very small vertical range. However all the virtual images produced by the cells are made to coincide with one another. The coincidence of the virtual images may be accomplished in several ways. ln the specific embodiment of the instant Vinvention described herein, the filaments in each cell are displacedvertically with respect tothe principal axis of their associated Fresnel lens such that rays of light traced from the optical center of the Fresnel lenses back through the corresponding filament in each cellconverge at a common point. The lamp laments are positioned with respect to the Fresnel lenses 'by adjustment screws tid as depicted in FIGS. l and 6. The Fresnel lenses are rall identically mounted with theirprincipal axes respectively perpendicular to the maior axis of the lens housing. An alternate method of causing the plurality of As an alternatel aanwas the Fresnel lenses and thus allows a virtual image virtual images to coincide is to incline the Fresnel lenses with respect to one another in such a manner that their principal axes converge at a common point. This method is illustrated schematically in FIG. 8. `Reference line d2 represents the longitudinal axis of the lens assembly dll. Fresnel lens 5@ oi cell 33 is mountedl with its principal axis 53 perpendicular to the reference line 52. The imageof lamp ttl of cell 33 appears at point 735. Lens fi@ of cell 32 is positioned such that its principal axis 545 intersects axis 53 of cell 33 at point 73. Thus the image of lamp` formed by lens 50 in cell 32 also appears at 73, thereby coinciding with the lamp image formed in cell 33. In like m-anner, the lens Sti of cells 3l, do and 35 would be positioned such that the virtual images formed thereby appear 'at 73. The lamp filaments in each cell are adjusted to lie in a plane which includes the principal axis of the lens through which they are imaged, said plane being perpendicular to the faces of the lens at the points of intersection. In this case the lamp lilaments in cach cell are placed so that they lie lin the same plane as the principal axis of the lens through which they are imaged. Since the virtual images formed by each lens are made to coincide with one another, the observer cannot distinguish which. virtual image he is seeing. The end effectfor the observer is to see a single virtual image through the particular pupil which lies in his line ol sight to the virtual image. The vertical viewing angle is depicted in FIG. l as the angle termed by the tion of the two planes dened by lines 7d, Elli, titl, and 7l.

f window, or more precisely, the system pupil 2li.

dll, and @l respectively. This angle is appronlnn l5 degrees.

The sensitivity ci the present system is measured the apparent vertical change in position ot the virtual image as seen by the observer in the indicator for a given change in vertical position ofthe aircraft. 'lille sensitivity varies directly with a change in the dista behind the lens at which the virtual image of the l at source appears For the specific application, a distance of approximately l50 vfeet has been found to be factory.` Distances somewhat greater than 150 feet itt-- crease the sensitivity but do not allow for reasonahlc deviations above or below. the optimum glide path distances somewhat less than 150 feet decrease the se tivity to such an extent that the pilot is unware of signalicant errors in his approach angle.

A practical iilament size has been found to be a single coil about thousandths or an inch in diameter placed with its axis perpendicular to the maior-axis of thelc assembly. The distance from the Preshnei lens to ti lamp is about two feet; themagnication of the sys is therefore approximately seventy-live i virtual image would have a linear height ci' about. inches but due to disturbances in the Fresnel surface also chromatic aberration, the images appear somewhat higher. ln the particular embodiment of the instant de vice, four lamps were used in each cell to obtain necessary candlepower and to insure that no appreciab loss of brilliance in the image of the line olsight wou be apparent to the observer if one lamp should fail.

As hereiubefore mentioned, lenticular spreaders are mounted in front of the Presnel lenses. 'lhese spreaders are made up of cylindrically ribbed pieces in which the axes of the ribs are mounted vertically. The action the cylindrically ribbed lenticular is well known in art and can most simply be considered as'that oi a sequence of prism angles with suliiciently frequent r tion so that they appear to an observer to be continu y ly adjacent. This sequence ol prism angles causes a lateral or horizontal spreading of the rays emergii lose discrimination in the horizontal azimuth and visible through a predetermined horizontal range. this instance the virtual image is visible from the steen of the carrier through an vangle of approximately degrees. This horizontal viewing angle is depicted FIG. l as the angle formed 'by the intersection of the two planes defined by lines lo, 7l, 72. and litt, till, d2, spectively. Since the cylindrical lenticular spreader lin a part of the system where the image as seen them is at a substantial distance, the skew vectors o" rays passing through the spreader-s is negligible and no distortion of the image results therefrom. As a resul" the action of the lenticular spl-cadera the observer can not distinguish the virtual images formed of the tour filaments in a particular cell.

The four adjacently placed filaments iu a particular cell must in the tinal analysis be imaged as a line ima and appear as a rectangular shaped area in the vi.

ila?

system pupil comprises a plurality of contigo pupils. Since the periphery of any lens is a L stop, the cell pupil is a function of both the lire.. el 50 and the lenticular spreader 'dit associated there However in the present system, the cell pupil is sub tially the same as the periphery of the Freenet This results from the substantially similar dimension ai the two lenses, the close spacing between them. and the location of the virtual image as seen through them. The aforementioned line image must he capable ci heing raised or lowered as hcrcinbcfore described. Consequently, the iield which must be imaged by includes all the possible positions of all the til hind that particular Freenet. With an assigns simple as a Fresnel lens it is not possible to achieve more than a compromisevsolution for a number of iield points. Such a compromise will allow adequate definition for the various pertinent parts of the ffield, Ibut this field will board lamps. Further. as the lamps are displaced vertically, they are moved by a cam toward or away from the `ilresnel lens so as to follow approximately the curvature of eld of the Fresnel lens as seen in a vertical section. This design lwas found to give optimum results for any Fresnel zone Iand lamp filament Icombination, thereby insuring negligible distortion on the face of the Fresnel lens when viewed at either short or long range. Additionally, the transition from the image of one set of lamps seen through the lens associated with that set of lamps to that ofthe adjacent set of lamps as seen through the adjacent lens is smooth and undistorted. Therefore if the pilot is high or low'with respect to the center or glide path position during landing, he will not see a jumpl1 in the image as he modiiies his position relative to the'system axis'.

While a preferred embodiment of the instant invention has beendescribed in connection with the landing of aircraft, it-must be understood that the foregoing description is meant to be illustrative only and is not limitative of the invention. The concepts employed in the optical device of the instant invention may `be utilized in various applications not specifically mentioned hereinyand vfurther modifications will suggest themselves to those skilled in the art. All such modifications as are in accord with the foregoing principles are therefore meant. to fall within the scope of the appended claims.

What is claimed is:

l. An optical device for displaying the image of a plurality ot' reference objectsto van observer, comprising a plurality of adjacent cells; each of said cells comprising a. referenceobject,v and a lens system positioned with respect to said reference object to form thereof a virtual image; said plurality of lens systems having contiguous pupils defining a system pupil of said optical device; said last 'pupil being oriented toward said observer; said plurality of lens systems and reference objects'being so disposed with respect to one another that the plurality of virtual images of said referenceobjects formed by said lens systems coincide with one another; said plurality of coincident virtual images appearing to said observer as a single virtual image visible through said system pupil.

2. An optical device as defined in claim l wherein means are provided for collectively displacing said reference objects with respect to their associated lens systems.

3. An optical device as defined in claim 2 wherein said means for displacing saidreference objects with respect to their associated lens systems comprises a common bracket for mounting said referenceobjects, said objects being adapted to movein a curved locus in response to the displacement of said common bracket, said curved locus approximating the curvature of iield of the lens systems through which'said reference objects are imaged.

4. An optical device for displaying the image of a plurality of reference objects to an observer comprising; a plurality of adjacent cells; each of said cells comprising a reference object, a first lens system for producing a magnified'virtual image of said object, and a second lens system disposed with respect to said first lens system for providing controlled dispersion of the rays of light emerging from said first lens system; said adjacent cells having contiguous pupils which comprise a system pupil of said optical devices; said plurality of rstlens systems and reference objects being so disposed with respect to 'closer to the Fresnel lens than the filaments of the iny one another that the plurality oi virtual images or" reference objects formed by said iirst lens systemischecide with one another; said plurality o coincident virtuel images appearing to the observer as a single virtual image visible through said system pupil.

5. An optical device for indicating to an observer an optimum path of travel comprising; a plurality of adjacent cells; each of said cells comprising a plurality of reference lights, a Fresnel lens for producing a magnified virtual image of said lights, and a lenticular spreader disposed with respect to said Fresnel lens for diaper-sing the rays of light emerging from-said Fresnel lens; said adjacent cells having contiguous pupils which comprise a system pupil of said optical devices; said last pupil being oriented toward said observer; said plurality ot .Fresnel' lenses and reference lights being so disposed with respect to one another that the plurality of virtual images of said reference lights formed by said Presnei lenses coincide with one another; said plurality of coincident virtual images appearing to said observer as a single -virtual image visible through said system pupil, whereby the position of said latter image may be viewed in relation to a datum marker; the apparent displacement of said datum marker with respect to said virtual as seen by the observer through the system pupil indiu eating a deviation from said optimum path of travel.

6. An optical glide path indicator for assisting a; pilot in lying an aircraft along a defined angle of approach to a landing area comprising an assembly suitably posi tioned with respect to the landing area; said assembly comprising a plurality of optical cells; each of said celia comprising a source of light, a rst lens so positioned with respect to said light source that a virtual image or' said source is formed, a second lens positioned with ren spect to'sad first lens for diffusing the rays ot iight emerging from said vrst lens; said optical cells having contiguous pupils defining a viewing window ot said glide path indicator; said window being oriented toward approaching aircraft; said plurality of optical cells having their first lenses and light sources oriented with respect', to one another in such a manner that the plurality Y virtual images produced by said cells coincide with. one

another; said plurailty of virtual images appearing through said viewing window as a single virtual image visible only through the lenses of the particular cell which lie in the pilots line of sight to said virtual image, whereby the position of said single virtual image can he viewed in relation to a xed marker placed in close proty with said glide path indicator assembly; the apparent displacement of said xed marker with respect to virtual image as seen by the -pilot being indicator-y or? deviation in the aircratts altitude trom said dehned angie of approach.

7. An optical device for aiding the pilot or an aircraft to follow al predetermined glide path while landing on an area of restricted size comprising an indicator assembly positioned on said landing area; said .indicator assembly comprising a plurality of cells; each of said cells comprisingan array of light sources, a Fresnel lens situated such that said array of light sources lies within the focal length of said Fresnel lens, said lens thereby forming u magnied virtual image of said sources, a lenticular.' spreader positioned with respect to said Fresnel lens for diffusing the light rays emerging from the Freshnel lens;

said plurality of cells having contiguous pupils defining a viewingvwindow of said optical device; said window being visible to the pilot of an aircraft approaching said landing area; said plurality of cells having their Fresuel lenses and light sources arranged in such a manner that the plurality of virtual images produced by said cells are coincident; said plurality of virtual images appearing v through said viewing window as a single virtual image I visible only through the pupils of the Fresnel lenses which lie in the pilots line of sight to said' virtual whereby the position of said latter image can be vierte by the pilot in relation toa'fixed marker; the1 apparent of a defined glide pathl to the pilot of an aircraft landing on the ight deck of a ship comprising an indicator assembly; said indicator assembly comprising a plurality of cells; each of said cells comprising an array of light sources, a Fresnel lens situated in such a manner thatv said light sources lie within the focal length of said' lFresnel lens, said lens thereby forming' a magnified virtual image of said sources, a lenticular spreader posivtioned with respect to said Fresnel lens for diffusing the light rays emerging from the Freshnel lens; said plurality of cells having contiguous pupils defining a viewing window of said optical device; said window being situated at one end of said assembly and being oriented toward oncoming aircraft; said plurality of cells having their Fresnel lenses and light sources arranged in such a manner that the plurality of virtual .images produced by said cells are coincident; said plurality of virtual images appearing to the pilot as a single virtual image through the viewingwindow; said plurality of light sources in the indicator assembly being mounted` on a common bracket; means for simultaneously changing Athe location of all said light sources with respect to their associated Fresnel lenses so as to modify the glide vpath indication Vas seenthrough said viewing window, whereby the alignment of said latter indication with a fixed marker is indicative of the aircraft`s approach along said defined glide path. A

Y 9. An optical deviceas defined in claim. 8 wherein the means for changing the location of said light sources with respect to the Fresnel lenses is controlled by sta-` bilization means in order to compensate for the pitching movement ofthe ship, said indicator assembly remaining in a fixed position on said fiight deck.

10. An optical device for aiding the pilot of an .aircraft to pursue a defined glide path while approaching the landing area comprising an indicator assembly mount.- ed on said area and adapted to be inclined with vrespect to a horizontal reference; said assembly comprising a plurality of cells; each of said cells comprising a plurality of lamp filaments as a sourceof. light, a Fresnel lens consisting of a segment of a spherical shell and forming a virtual image of said lamp filaments, a cylin- Adrical ribbed lenticular positioned with respect to said Fresnel lens and adapted for horizontally spreading the light -rays emerging from said Fresnel lensjmeans for displacing said groups of lamp filaments collectively with respect to their associated Fresnel lenses; said plurality of cells having contiguous pupils forming a viewing window of said optical device; said window being situated at supporting members, said members being adapted to move iii? one end of said indicator assembly and being visioie said cells are coincident; said plurality of' virtual images appearing to the pilot. as a single image through the viewing window ot said indicator assembly, whereby the position of said single image can be compared to a fixed marker mounted adjacent to said indicator assembly; a fixed marker directly visible to the pilot and mounted adjacent to said indicator assembly; the apparent displacement of said fixed marker with respect to said virtual image as seen through the viewing window by the pilot being indicatory of deviation in the aircrafts attitude with respect to said defined glide path.

l1. An optical device as defined in claim l0 wherein said plurality of lamp filaments contained in each Celi are supported by a member having-lamp mounting positions arranged in a curved locus approximating the curvam ture of field of the Fresnel lens through which said filaa ments are imaged.

12. An optical device as defined in claim li. wher said means for displacing said groups of lamp filante comprises a common bracket for mounting said la in a curved locus in response to the displacement of sai bracket, said curved locus approximating the curvature e field of the P resnel lens through which said lamp t... ments are imaged.

13'. An optical device for displaying the image of plurality of reference objects to an observer, compris a plurality of adjacent cells; each of said cells compil ing a reference .object and a lens system positioned respect to said reference object to form thereof an imU age; said plurality of lens systems having contiguous pupils defining. a system pupil of said optical device; said last'pupil -being oriented toward said observer; said plurality of lens systems and reference objects being so disposed with respect to one another that the plurality of images of said reference objects formed by saidlens systems coincide with one another; said pluraiity ofi coincident images appearing to said observer as a single References Cited in the file of this patent UNITED STATES PATENTS Bernard Apr. 20, 1920 Villiers ian. 2, 1935: Goedhart ...me Mar. l2, lgiii' 

